We provide free advertising every day in the products that we use. Do you ask for your Starbucks coffee or tea in a plain cup? Do you cover up the name on your soft drink can? Do you tape over the name on your television set or disguise your MP3 player?
It's all part of the capitalist experience. Nearly everything is branded.
When it comes down to it, most people don't care what we use or where we bought it unless they're curious and want to know more.
If someone asks you where you bought an older camera, do you tell them "that auction site" -- and if pressed further, you remain silent? Of course not. Or at least, I hope not.
I really think this reluctance to say eBay, the Goodwill, a charity or thrift shop or whatever is unnecessary.